Subscription-television audioreceiving system



w. QUAN ETAL SUBSCRIPTION-TELEVISION AUDIO-RECEIVING SYSTEM FiledJunevls. 1961 June l, 1965 www INVENTORS.

Patented .lune l, i965 aalsmeer sUnsenierroN-rntnvrsrois .sunronnenrvnsnsrsrnsi 'Wasson Quan and 1rdiehard CC. Cardin, 5r., Los Angeles,

This invention relates to subscription-television systems and, moreparticularly, to an improvement in audio-receiving circuits employed insubscription television.

Present-day commercial television receivers employ the intercarriermethod of sound reception. ln this method, both picture and sound IFsignals are amplified in all the picture iF stages and are passedthrough the picture second detector. The second detector produces in itsoutput a 4.5 mc. signal, which is the beat frequency between the pictureand sound 1F carriers, commonly known as the intercarrier signal. Thisintercarrier signal arises from two carriers, one amplitude-modulatedand the other frequency-modulated. The deviation of thefrequency-modulation component is identical to that of the soundcarrier, and, accordingl by passing this intercarrier signal through theusual limiters and detectors, the frequency-modulation components areconverted into the desired audio-frequency components, and the amplitudemodulation of the intercarrier signal is prevented from affecting theaudio-signal components. lt would therefore appear that, in order toreproduce audio signals, two carrier signals are required.

In an application for a Subscription-Television System, Serial No.77,184, filed December 20, 196C', by Carl A. S. Akrell, now U.S. PatentNo. 3,104,280, which is assigned to a common assignee, there isdescribed a closed-circuit subscription-television system. In thissystem, the transmitter sends to the receiver video program signals,audio program signals, control signals which include pricinginformation, recording information, barker audio signals, and a pilotcarrier signal. At a subscriber receiver, there is provided anattachment which utilizes the pilot carrier signal and the controlsignals for establishing the price which must be paid for viewing theprogram. Upon payment of this price, the output of the local oscillatoris modulated by the video and audio program signals so that they appearon a carrier which can be applied to the antenna terminals ot thereceiver. The receiver can then process these signals exactly in themanner of the usual television signals received by its antenna.

The barker audio signals constitute a source of information concerningthe merits of the program for which payment is being sought, as well asany other information of interest to the subscriber. Since the barkeraudio signals, which are transmitted as frequency-modulated signals, donot accompany a video carrier, the problem is presented as to how toenable a commercial television receiver which uses intercarrier sound toreproduce these barker signals without such additional carrier beingprovided. In the Akrell system mentioned previously, the pilot carrierserves this function. It together with the barker signals which arefrequency-modulated on a carrier are fed to the television receiver,which can then process these signals in the manner of audio signalswhich usually accompany any video broadcast.

An object of this invention is the provision of an arrangement forenabling a receiver in a subscription-tele- Vision system to reproduceaudio signals from frequencymodulated signals, without the necessity oftransmitting two carriers required for deriving audio signals in theintercarrier sound system of the receiver.

Another object of this invention is the provision of a novel arrangementfor processing audio signals, frequency-modulated on a carrier, in asubscription-television ysystem prior to their being introduced into thesubscriber receiver, so that they may be reproduced, either by areceiver having an intercarrier sound system or by a receiver which hasa double IF system.

Yet another object of this invention is the provision of a novel andsimple arrangement for processing frequencymodulated audio signals in anattachment for a television receiver in a manner so that the receivermay reproduce these signals, regardless of whether or not anothercarrier has been transmitted therewith.

In a subscription-television system of the type described and claimed inthe Akrell application, a local oscillator is provided in the receiverattachment for the purpose of converting the carrier on which theprogram video and program audio are transmitted to a frequency which canbe processed by the standard commercial television receiver. This occurswhen proper payment has been made for the program which is desired to beviewed. In accordance with this invention, it has been found that bytransmitting the barlcer audio as a frequency modulation on a carrierhaving a frequency of 4.5 mc., with a maximum deviation of m25 kc., thesignal can be processed in the same converter as is employed to processthe program video and audio, where it is mixed with the output of thelocal oscillator. The output of the converter comprises two signals, oneof these being a new carrier which carries the FM audio modulation andthe other being the unmodulated oscillator output. The intercarriersound system of the receiver can then process these signals in the samemanner as the normal intercarrler sound signals, and the receiver willreproduce the barlrer audio. Receivers of the older variety, whichemploy two separate IF strips, have no difficulty in reproducing thebarker audio signals, either.

The novel features that are considered characteristic of this inventionare set forth with particularity in the appended claims. The inventionitself, both as to its organization and method of operation, as well asadditional objects and advantages thereof, will best be understood fromthe following description when read in connection with the accompanyingdrawings, in which:

FGURE l is a block diagram of a subscription-television system of thetype with which this invention functions, which is shown in order toafford an understanding of this invention; and

FlGURE 2 is a block diagram illustrating an embodiment of thisinvention.

Referring now to FIGURE l, a closed-circuit subscription-televisionsystem of the general type described in the previously mentionedapplication to Akrell includes a transmitter lll, which transmitsprogram video and program audio on a nonstandard carrierthat is, onewhich cannot be processed by the usual commercial television receiver.In addition, the transmitter transmits pricing signals for enabling aprice to be set up at a subscribers receiver indicative of the amountrequired to be paid to view the program. In addition, the transmittedwill transmit a barked audio signal which is frequency modulated on acarrier located, for example, at 4.315 mc./s. In addition, a pilotcarrier is transmitted in order to enable the barker audio signals to bereproduced by the receiver. The pilot carrier may be at a frequency of,for example, 8.815 mc./s. and has no modulation.

The transmitter l@ is connected over a line 12 to the subscriberreceivers, each of which will have an attachment 14, which includes theapparatus shown within the dotted rectangle. Such attachments willinclude a coinbox control circuit 16, which has the necessary circuitryfor separating the pricing signals from the other signals being receivedand for applying them to a coinbox 13, whereby a price for viewing theprogram is established. An RF amplilier 20 is connected to the line.

lgram audio signals.

A Selector switch, having separate switching decks 21A, 21B,simultaneously tunes the RF amplifier 20 and the local oscillator 22.The selector switch decks 21A and ZIB in the position shown will enablethe barker and pilot carrier signals to pass through the RF amplifierand will tune the local oscillator to a frequency such as 86.065 mc./s.

A converter 24 receives the output of the RF amplifier 2f) and theoutput of the local oscillator 22. This converter can convert theV pilotcarrier to a frequency of 77.25 mc./s. and the barker carrier to afrequency of V81.75 rnc./s. These signals are then applied to an outputcircuit 26, which couples them to the antenna terminals of the receiver28, which can then process these signals in the normal manner, wherebybarker audio may be heard by a subscriber.

When the selector switches 21A, 21B are connected to the other positionshown in the drawings, the RF amplifier is tuned to receive the programvideo and pro- The local oscillator 22 is tunedV to a frequency forconverting the video and-audio carriers to a frequency which thereceiver 2S can suitably process. However, the local oscillator is notpermitted to oscillate at this time until the coinboX 18 has receivedpayment of the price demanded. At this time, it enables the localoscillator 22 to commence oscillation. The converter 24 will thenprocess the video and audio program signals, apply them to the outputcircuit 26, which, in turn, properly couples them to the receiver 2S tobe re produced. Y

In accordance with this invention, no other carrier need be sent by thetransmitter in order to enable the frequency-modulated barker audioVsignals to be reproduced at the receiver. Instead, as shown in FIGURE2, at the transmitter 30, barker audio from a source 32 is applied to amodulator 34 to frequency modulate the output of a 4.5 mc./s. oscillator36. This carrier is distributed to Vsubscriber receivers over aline 3S.

At each receiver, there is an attachment which is identical 4with theone represented in FIGURE 1, the difference being only in theaddition ofa 4.5 mc. filter, and .the Vtuning of the circuits for handling thebarker structure shown in FIGURE 1, which is not essential to anunderstanding of the invention and is omitted in FIGURE 2. Wheninformation with respect to a program is desired, the selector switch41A, 4fB, 41C is turned to the Aposition shown in the drawing. The otherposition of the switch is used for receiving a program, as previouslydescribed. The radio-frequency amplifier amplifies the 4.5 mc./s.frequency-modulated carrier signal received `over the line 38. Switchsection 41C in the position shown connects the output of theRFamplier'42 to a 4.5 Inc/s. bandpass filter 42; in its other position,the

Vfilter 42 is bypassed and the output of the RF amplfier Vvalue ysuchthat the amplitude of the unmodulated carrier which passes through theconverter 34 is larger than the amplitude of the 83.25 mc. convertedfrequency. Thus, the output circuit 48 will have applied to it anunmodulated carrier of 87.75 mc. and a frequency-modulated carrier'of8325 mc. These two frequencies are then applied to the input circuits ofthe television Vreceiver.

The output of the video detector of a television receiver will contain a4,5 mc. frequency-modulated carrier. This is the intercarrier signalfrequency to which the circuits of the receiver can respond in order todemodulate this signal of the information carried thereon. It willtherefore be seen that the barker audio, which contains programinformation, may be produced at the television receiver by justtransmitting a frequency-modulated carrier at 4.5 mc./s. Since a carrierfrequency is required in any event, no additional equipment is requiredat the transmitter. Also, a local oscillator is required at the receiverattachment in any event, so, aside from an inexpensive 4.5 mc./s.bandpass filter, nothing further is required at the receiver. Inaddition to the advantage in eliminating the requirement for anadditional carrier, another advantage is that the local oscillator maydrift as much as i.25 rnc./s., but the 4.5 mc./s. separation requiredfor intercarrier detection will always be maintained. Furthermore, withthis invention, less bandwidth is required for transmitting asubscription-television program over a line. This is an important factorwhere several subscription-television programs are sought to betransmitted.

From the foregoing description, it should be appreciated that there hasbeen described an arrangement for a closed-circuitsubscription-teievision system wherein no second carrier signal is sentby the transmitter in order to achieve reproduction of the audiosignalsin an intercarrier Vsound system. By tuning the local oscillatorto oscillate at a frequency which will place the audio carrier withinany one of the regular television channels and adjusting the carrieramplitude, a receiver can process the signals in a normal manner. Itshould be appreciated that the examples of frequencies given are by Wayof illustration, and not by way of restriction.

We claim:

1. In a subscription-television system of the type wherein a transmittertransmits program video and audio signals on a carrier which is notsuited for processing by a receiver to subscriber receivers havingattachments includingV a local oscillator and a converter for convertingthe nonstandard program and audio carrier to a standard video and audiocarrier which can be processed by said receiver, the improvementcomprising transmitting audio signals modulated on a 4.5 mc. carrierfrom said transmitter to said subscriber receivers, tuning said localoscillator to a frequency such that a carrier at a frequency 4.5 mc.less than said local oscillator frequency together with said local'oscillator frequency can be processed by the intercarrier soundcircuits of said receiver, mixing said local oscillator output togetherwith said 4.5 mc. frequency-modulated signals in said converter toderive an output therefrom comprising said unmodulated local oscillatorsignals and a frequencymodulated carrier at 4.5 mc. frequency less thanthe frequency of said local oscillator signals, said local oscillatorhaving its amplitude adjusted to insurel that the unmodulated carrieroutput of said converter has an amplitude greater than thefrequency-modulated carrier output of said converter, and applying saidconverter output to said receiver whereby it is enabled to reproducesaid audio signals. Y

2. A subscription-television system comprising atransmitter having meansfor generating audio signals, means for generating a carrier having afrequency of 4.5 rnc/S.,

Y means for frequency modulating said audio signals on said carrier, areceiver having an intercarrier sound-demodulating system, means fortransmitting said frequencymodulated carrier to saidreceiver, means atsaid receiver for generating a local unmodulated carrier having a fre-Vquency which, when combined with a frequency-modulated carrier having afrequencyV which is 4.5 mc./s. different, can be processed by saidreceiver intercarrier sound system, means for mixing saidfrequency-modulated carrier and said local carrier, and means forapplying said means for mixing output to said receiver intercarrierVsound-demodulating system.

3. In a subscription television system of the type wherein a transmittertransmits program audio and program video signals on a firstnon-standard carrier and second audio signals on a 4.5 megacycle carrierto a subscriber having a converter connected to his television receiverfor enabling said receiver to intelligibly process said second audiosignals in the absence of payment by said subscriber, and for enablingsaid converter to convert said program video and program audio signalsto a form whereby said receiver may intelligibly process them uponpayment by said subscriber, the improvement in said converter comprisingan input terminal to Which said program video, said program audio andsaid second audio modulated upon a 4.5 megacycle carrier is applied,oscillator means in said converter for generating a local unmodulatedcarrier having a frequency which when combined with a frequencymodulated carrier having a frequency which is 4.5 megacycles per seconddifference, can be processed by said receiver inter-carrier soundsystem, means for mixing said 4.5 megacycle frequency References Citedby the Examiner UNITED STATES PATENTS 2,875,274 2/59 Farr 178-5.8

DAVID G. REDINBAUGH, Primary Examiner.

STEPHEN W. CAPELLI, Examiner.

2. A SUBSSCRIPTION-TELEVISION SYSTEM COMPRISING A TRANSMITTER HAVINGMEANS FOR GENERATING AUDIO SIGNALS, MEANS FOR GENERATING A CARRIERHAVING A FREQUENCY OF 4.5 MC./S., MEANS FOR FREQUENCY MODULATING SAIDAUDIO SIGNALS ON SAID CARRIER, A RECEIVER HAVING AN INTERCARRIERSOUND-DEMODULATING SYSTEM, MEANS FOR TRANSMITTING SAIDFREQUENCYMODULATED CARRIER TO SAID RECEIVER, MEANS AT SAID RECEIVER FORGENERATING A LOCAL UNMODULATED CARRIED HAVING A FREQUENCY WHICH WHENCOMBINED WITH A FREQUENCY-MODULATED CARRIER HAVING A FREQUENCY WHICH IS4.5 MC./S. DIFFERENT, CAN BE PROCESSED BY SAID RECEIVER INTERCARRIERSOUND SYSTEM, MEANS FOR MIXING SAID FREQUENCY-MODULATED CARRIER AND SAIDLOCAL CARRIER, AND MEANS FOR APPLYING SAID MEANS FOR MIXING OUTPUT TOSAID RECEIVER INTERCARRIER SOUND-DEMODULATING SYSTEM.